The molecular basis of the interaction between collagen and platelets will be investigated. Cyanogen bromide peptides of collagen will be assayed for their ability to inhibit activation of platelets by collagen, or for their capacity to activate platelets. Biologically active peptides will be further digested with proteolytic enzymes in order to obtain the smallest, biologically active, peptides. Also, synthetic peptides will be prepared in order to investigate structural parameters required for recognition by, and interaction with, platelets.